refactor(web): extract design tokens to tokens.json source of truth

The Flutter client (#356) needs to consume the same FabledSword tokens
the web SPA uses. Move the data into a structured tokens.json file and
generate tokens.generated.css from it on every Vite build. The Flutter
side gets its own generator pointed at the same JSON.

No visual change — generated CSS matches the previous hand-written file.

Also installs @types/node devDependency: tsconfig already declared
"types": ["node"] but no Node builtins were referenced in TS until now,
so the missing types were latent. The new vite.config.ts plugin imports
node:child_process, surfacing the gap.

web/vite.config.ts

@@ -1,8 +1,16 @@
 import { sveltekit } from '@sveltejs/kit/vite';
 import { defineConfig } from 'vite';
+import { execSync } from 'node:child_process';
+
+const tokensPlugin = {
+  name: 'minstrel-tokens',
+  buildStart() {
+    execSync('node scripts/tokens-to-css.js', { stdio: 'inherit' });
+  }
+};
 
 export default defineConfig({
-  plugins: [sveltekit()],
+  plugins: [tokensPlugin, sveltekit()],
   server: {
     port: 5173,
     proxy: {